I think selfkill is often used in games and suicide in real life. Is that correct?
Suicide is killing oneself intentionally.
Selfkill is only in use as slang in computer games. As well as controller ochestrated avatar death, it also includes instances where your avatar dies accidentally, e.g. falling to its death due to a misstep or rocket jumping with too little health.
Garner’s Dictionary of Legal Usage list self-killing (notice the hyphen) as synonymous with suicide. (So legally they are the same thing.)